The AUM sound navigates chakra energy through your left (A) channel, right (U) channel and centers your energy through the center (M) channel. It helps to achieve effortless meditation state. If you ever wondered why monks or any other group of people who meditate say OM and not AUM, here is the answer.
Step 1
Position your mouth as you would say the vowel "U".
Step 2
With your mouth position unchanged, start pronouncing AUM. This is where the throathy "O" comes from.
Step 3
Finish with "M" as deep humming.